The present invention relates to the field of apparatus and methods intended to offer support to a medical operator in the performance of a medical procedure.
More in particular, the present invention relates to an apparatus and to a method for mapping a three-dimensional space in medical applications for diagnostic, surgical or interventional medicine purposes.
It is widely known how, during the performance of a medical procedure, devices are often used that are capable of providing real time images of body parts or internal organs of the patient.
These devices are used, for example, to allow the medical operator to determine optimal operational positioning of medical instruments (e.g. catheters, needles, cutting instruments, etc.) to be used in the medical procedure being performed.
Fluoroscopes are the devices most commonly used to obtain real time images of the patient's internal anatomy, given that they are characterized by relatively limited dimensions, which allow them to be used easily in proximity of the operating field of the medical operator.
A common fluoroscope is illustrated schematically in FIG. 1.
The device (reference 50) comprises a main body 51 and a C-shaped arm 52, movable with six degrees of freedom with respect to the main body. An X-ray source 54 and a fluorescent screen 53 are secured at the opposite end of the arm 52.
To record images of internal organs or body parts, the arm 52 is positioned in such a manner that the patient's body is located in the space between the source and the screen. Typically, the screen 53 is operatively associated with a video camera that allows the images acquired to be reproduced easily on monitors.
Other types of apparatus for real time image acquisition of the patient's anatomy, without the use of ionizing radiation, are available in the state of the art. One example of these is represented by common ultrasound probes.
The images supplied by a fluoroscope or by an ultrasound probe are normally two-dimensional and without absolute references.
Therefore, in order for these images to effectively be of assistance during the medical procedure, it is necessary to map the three-dimensional space in which the patient's body is located, in order to learn the coordinates of its points (and therefore the position of the patient's internal organs and body parts) relative to an absolute reference system.
Some mapping methods, such as the one described in the patent application EP1942662, consist of recording stereoscopic images of the patient's body and establishing a correlation with images of the patient's body, recorded in a pre-operative phase and provided with predefined absolute references. Appropriate image recognition algorithms are used to establish this correlation.
Mapping methods of this type are generally lengthy (requiring over 30 minutes) and must be carried out by specialized personnel, who are normally not part of the medical team.
Moreover, the reliability of these methods is limited, given that often the position of the internal organs of the patient is not the same in the pre-operative phase and during performance of the medical procedure.
Other mapping methods, such as the one described in the U.S. Pat. No. 6,167,292, consist of the use of marker elements rigidly associated with the patient's body, which define a reference system of the three-dimensional space of interest. At the beginning of the medical procedure, the marker elements are “touched” by the operator using a pointer operatively connected to a computerized device which performs matching algorithms to register the three-dimensional reference system, defined by the marker elements, with a known reference system.
Although ensuring high precision, these mapping methods are relatively laborious to use in the field.
It is also inconvenient to secure the marker elements integrally to the patient's body, given that these can in fact undergo shifting due to sudden or imprudent movements of the patient. Moreover, these foreign bodies are a considerable source of discomfort for the patient, who is obliged to suffer their presence for relatively long periods of time.
The patents EP1910040B1 and U.S. Pat. No. 6,349,245B1 describe apparatus for mapping a three-dimensional space wherein a robotic arm, provided with a video camera, is used to automatically detect the position of marker elements, integral with the patient's body. Computerized means calculate the coordinates of the marker elements relative to a known reference system.
Although having the disadvantages linked to the use of marker elements operatively connected to the patient's body, these apparatus allow a reduction of the times required to perform the mapping operations.
However, they are characterized by relatively low precision, given that the position of each marker elements is calculated starting from a detection that is not stereoscopic.
Further mapping methods consist of placing the marker elements on a target in a fixed position, not operatively associated with the patient's body.
These methods consist of recording the target from different positions, recognizing homologous points identifiable in the different views and mapping the three-dimensional space of interest on the basis of geometric relations existing between the homologous points identified.
In order to be performed correctly, these mapping techniques require the images with which the target is recorded to be perfectly isocentric and the target to remain stationary in the space during recording.
Due to the constraints described above, it is difficult to use a common fluoroscope to record images of the three-dimensional space of interest.
In fact, to obtain isocentric images, the fluoroscope must be locked along at least five axes of motion, resulting in a considerable reduction in its operating mobility.
It is therefore extremely difficult, if not impossible, to record images of relatively large three-dimensional spaces.
In the state of the art, computer-assisted navigation devices are available, which are aimed at increasing the visual perception of the medical operator during performance of a medical procedure.
These devices are capable of providing three-dimensional reconstructions of the patient's body parts, which are generally obtained by integrating images acquired in the field with visual structures generated by a computer.
As these navigation systems are generally operatively associated with video camera stereoscopic systems, they can be used to map a three-dimensional space relative to a proper absolute reference system.
The U.S. Pat. No. 7,561,733 describes a mapping method which comprises the use of a pair of video cameras provided with marker elements to record the three-dimensional space of interest. The absolute position of these video cameras is obtained by means of a navigation system. The limitation deriving from use of video cameras which allow only images from outside the patient's body to be acquired is evident.
The U.S. Pat. No. 7,251,522 describes a mapping method which comprises the use of marker elements secured integrally to the end of the C-shaped arm of the fluoroscope, in such a manner as to be framed during recording of the three-dimensional space. The absolute position of the C-shaped arm in the space is obtained by means of a navigation system.
A considerable limitation of this technique consists in the fact that the fluoroscope recordings are themselves subject to non-linear distortions, often caused by external electromagnetic fields. These distortions can cause errors to occur in the mapping operations.
In addition to the drawbacks mentioned, the methods described above also have the disadvantage of being of laborious practical implementation, given that they require the presence of a navigation system. In fact, the use of a navigation system generally constitutes a complex activity, which requires a high level of training and which often must be operated by specialized personnel.